SUMMARY: Seasonal grazing of the fish Sarpa salpa (L.), the urchin Paracentrotus lividus Lamarck and the isopods Idotea spp. was compared with the C/N ratio of adult and intermediate leaves and epiphytes of Posidonia oceanica (L.) Delile, collected at three different depths. Despite seasonal differences in grazing, herbivores showed preferences throughout the year for adult leaves with more epiphyte and higher N contents. The maximum grazing on adult and intermediate leaves was observed in September and in June for fish and in March for urchins, whereas it was irregular for isopods. Grazing by the three herbivores was not related to their preference for leaves or epiphytes, notwithstanding the seasonal differences in their C and N contents. We concluded that herbivores show no preference for food type throughout the year and that seasonal consumption of P. oceanica is related mainly to herbivore behaviour.Key words: grazing, C/N ratio, seagrass, epiphytes. *Received February 16, 2000. Accepted May 15, 2001. 1996 and showed that the percentage of leaf production removed by herbivores in summer was correlated with both leaf specific growth rates and leaf production per shoot (Cebrian and Duarte, 1998).Differences in grazing might also be explained by different behaviour of the grazers. Massive schools of the fish S. salpa actively feed on P.oceanica leaves in Summer to accumulate reserves for reproduction. In winter, adults migrate to greater depths, whereas young fish, in shallow waters, eat preferentially small crustaceans (Bini, 1968;Tortonese, 1975, Francour, 1997 and turf epilithic algae (Havelange et al., 1997).P. lividus forms true populations in P. oceanica meadows, where high densities may have a heavy impact on the meadow (Kirkman and Young; Nedelec and Verlaque, 1984). Even though the urchins reproduce throughout the year (Tortonese, 1965;Fenaux 1968), major spawning is concentrated in spring and summer (Fenaux 1968;Azzolina and Willsie, 1987) and is related to the lowest consumption of seagrass (Semroud and Kada, 1987). While the young urchins feed on both rhizomes and leaves, the adults (>2 cm diameter) have a low-specialised diet and graze preferentially, on the highly epiphytized distal part of the leaves at nigth (Nedelec and Verlaque, 1984;Zupo and Fresi, 1984).Little is known about the behaviour of the isopods. The diet of the isopods I. baltica balsteri was investigated by Lorenti and Fresi (1982), who observed prolonged survival of the animal feeding on living leaves of P. oceanica.Until now, it is not clear whether seasonal grazing is related to leaf or epiphyte quality of food or depends on other factors. The aim of the present work is to assess the relationships between grazing pressure and food availability and C and N contents, both in time and space. For this purpose three stations along a depth gradient were observed during one year. Two levels of food were considered: a) leaves (adult and intermediate) and b) epiphytes (divided into major taxa). Seasonal variations in food quality were ...

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The organic content of sediments, often considered as an important trophic source for the benthos, can be used as a measurement of the trophic status of marine ecosystems. Soft-bottom communities were studied between Leghorn and Elba Island, from 5 to 500 m depth. Total biomass and trophic structure (percent dominance of trophic guilds) were related to organic carbon content and C/N ratio of sediments. Sediment organic matter, depending on its quantity and quality, could act as a food source or a stress source for the community.

Abstract. "1"he origin, quality and pathways of particulate organic carbon (POC) were studied from May 1991 to May 1995 in a submarine cave (Grotta Azzurra, Tyrrhenian Sea, Italy) with warm sulphur springs that support dense mats of sulphur-oxidizing bacteria. Multifactorial sampling designs were used to specifically address: (I) differences in the quantity and quality of suspended and sedimenting particles in two distinct regions of Grotta Azzurra, a weakly-illuminated outer region (Central Hall) and an innermost dark region (Snow Hall) characterized by the presence of sulphur waters; (2) the composition and fluxes of pamculate material above and below the sulphurous boundary. The water and sediment trap samples were analysed for total particles. POC, pamculate organic nitrogen (PON), chlorophyll a (Chl a) and phaeopigments (Phaeo). The nficrobial mats were assayed for carbon fixation and RubisCo activity. Stable carbon isotope ratios of the bacteria, benthic fauna and sediments were measured. The overall amount and flux of POC did not differ between the two regions of the cave. By contrast photosynthetic pigments decreased significantly from the outer to the inner region. The average POC:PON ratios of suspended and sedimenting material were lower than 10.2, and there was no apparent ageing or degradation from the Central Hall Io the Snow Hall. Fluxes of POC above the boundary were on average 23.8% of fluxes measured below the boundary, and no Chl a was detected above the boundary. The mats of sulphur-oxidizing bacteria had a 13C depletion of -30 to -3 I%o, providing a marker for tracing POC from this source. The majority of the benthic animals showed ~13C from -20 to -24%0. Some polychaete worms and echinoderms were more depleted (-25%o), indicating greater consumption of bacterial carbon, while sponges were not depleted compared with the benthos of the control cave (213C -18 to -19%c). It is estimated that bacteria supply about 31% of the suspended POC in the Snow Hall. A larger input may be available to ammals living close to the bacterial maJs and to those in the more sulphurous Grotta Sulfurea cave.

A study of the granulometric, mineralogical and chemical composition of surface sediments and suspended particulate matter in the coastal area between Varazze and Cape Noli (Ligurian Sea), provided useful information on transport and sedimentation processes in the area . Sediments samples from the shelf were highly heterogeneous, ranging from pelites to sands . Minerals typical of individual river basins were found close to river mouths, indicating a limited sediment transport along the coast . Chemical and textural characteristics of the suspended particulate matter indicated that the longshore sediment transport is influenced by the presence of a submarine canyon ; material coming from the east, following the Ligurian current, is partially diverted offshore along the canyon axis . The coastline pattern, some harbor artifacts, and the peculiar morphology of the shelf are all factors controlling the direction of sediment transport . 17